Try this - grab your expansion tank cap, and try to push it back and forth (towards the engine and away from it). See if it moves. If it does, there are some rubber mounts for the radiator that hold it in place! And they may be shot. I am pretty sure item #12 in the diagram below is a screw type mount, that can be raised and lowered to secure everything in place. This may be the source of some of the noise.